INSECTS AND AKACHNIDA. 233 



conformation of tnese organs, there is no occasion here to dwell upon 

 them longer than to specify such as are most interesting to the Micro- 

 scopist: Coleoptera, Brachinus, Calathus, Harpalus, Dytiscus, Staphyli- 

 nus, Philonthus, Elater, Lampyris, Silpha, Hydrophilus, Aphodius, 

 Melolontha, Cetonia, Curculio; Orthoptera, Forficula (Earwig), Blatta 

 {Cockroach) ; Lepidoptera, Sphinges (Hawk-moth), and Nocturna 

 (Moths) of various kinds, the large ' plumed' antennae of the latter being 

 peculiarly beautiful objects under a low magnifying power; Diptera, 

 Culicidae (Gnats of various kinds), Tipulidae (Crane-flies and Midges), 

 Tabanus, Eristalis, and Muscidae (Flies of various kinds). All the larger 

 antennae, when not mounted f dry ' as opaque objects, should be put up 

 in Balsam, after being soaked for some time in turpentine; but the small 

 feathery antennae of Gnats and Midges are so liable to distortion when 

 thus mounted, that it is better to set them up in fluid, the head with 

 its pair of antennae being thus preserved together when not too large. 

 A curious set of organs has been recently discovered in the antennae of 

 many Insects, which have been supposed to constitute collectively an 

 apparatus for Hearing. Each consists of a cavity hollowed out in the 

 norny integument, sometimes nearly spherical, sometimes flask-shaped, 

 and sometimes prolonged into numerous extensions formed by the folding 

 of its lining membrane; the mouth of the cavity seems to be normally 

 closed-in by a continuation of this membrane, though its presence can- 

 not always be satisfactorily determined; whilst to its deepest part a nerve- 

 fibre may be traced. The expanded .lamellae of the antennae of Melolontha 

 present a great display of these cavities, which are indicated in Fig. 427, 

 A, by the small circles that beset almost their entire area; their form, 

 which is very peculiar, can here be only made out by vertical sections; but 

 in many of the smaller antennae, such as those of the Bee, the cavities can 

 be seen sideways without any other trouble than that of bleaching the 

 specimen to render it more transparent. 1 



629. The next point in the organization of Insects to which the 

 attention of the Microscopist may be directed, is the structure of the 

 mouth. Here, again, we find almost infinite varieties in the details of 

 conformation; but these may be for the most part reduced to a small 

 number of types or plans, which are characteristic of the different orders 

 of Insects. It is among the CoUoptera, or Beetles, that we find the 

 several parts of which the mouth is composed, in their most distinct 

 form; for although some of these parts are much more highly developed 

 in other Insects, other parts may be so much altered or so little developed 

 as to be scarcely recognizable. The Coleoptera present the typical con- 

 formation of the mandibulate mouth, which is adapted for the prehen- 

 sion and division of solid substances; and this consists of the following 

 parts: 1, a pair of jaws, termed mandibles, frequently furnished with 



1 See the Memoir of Dr. Hicks ' On a new Structure in the Antennae of Insects,' 

 in " Trans, of Linn. Soc.," Vol. xxii., p. 147; and his Further Remarks,' at p. 383 of 

 the same volume. See also the Memoir of M. Lespes, ' Sur 1'Appareil Auditif des 

 Insectes,' in "Ann. des Sci. Nat.," Ser. 4, Zool., Tom. ix., p. 258; and that of M. 

 Claparede, * Sur les pretendus Organes Auditifs des coleopteres lamelhcornes et 

 autres Insectes,' in "Ann. des. Sci. Nat.," Ser. 4, Zool., Tom. x., p. 236. Dr. Hicks 

 lays great stress on the * bleaching process,' as essential to success in this investi- 

 gation; and he gives the following directions for performing it: Take of Chlorate 

 of Potass a drachm, and of Water a drachm and a half; mix these in a small wide 

 bottle containing about an ounce; wait five minutes, and then add about a drachm 

 and a half of strong Hydrochloric Acid. Chlorine is thus slowly developed; and 

 the mixture will retain its bleaching power for some time. 



